io_uring: fix punting req w/o grabbed env

It's not enough to check for REQ_F_WORK_INITIALIZED and punt async
assuming that io_req_work_grab_env() was called, it may not have been.
E.g. io_close_prep() and personality path set the flag without further
async init.

As a quick fix, always pass next work through io_req_task_queue().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>